4 Wheel Drive Systems: Their differences...

**wolfpack** · May 22nd, 2003 09:47 AM

ALL WHEEL DRIVE

All wheel drive is exactly what it says, it drives all 4 tires of a vehicle when running all time when the vehicle is in use, the difference is that it does not "LOCK" the front and rear differentials of the vehicle mechanically due to what is called the "Tight Turn Braking Phenomena" this happens when both front and rear differentials are Syncronized in Distribution of torque to both front and rear Diffrentials on a vehicle equipped with a Central Diff Lock which is engaged. When making a u turn on pavement a vehicle with the Central Diff lock engaged, the vehicle will experience a braking effect due to the difference (Hence the term differential lock) in the distance travelled by the front and rear tires, This is similar to why a 2 wheel drive vehicle is not equipped with a locking device to syncronize both left and right tire, continous usage of your diff lock on pavement will eventually lead to severe drive train damage and extreme tire wear.

It is for this reason why All Wheel drive came into being, an all wheel drive system does not "Syncronize" the spin of the front and the rear diffs to avoid the tight turn braking phenomena, and provides the superior traction and handling afforded by "4wd" minus the thight turn braking effect. This is made possible by a British development called "Vicous Coupling" It is a front and rear diffrential "syncronizing" system using Hydraulic fluids to propel the Front and/or rear diffs of the vehicle. Since the propeling medium is fluids it does not "LOCK" the front and rear Diffs and drive torque can be manipulated to distribute more torque to the front or rear diffs of the vehicle which is offered in some Rally cars, on production vehicles the manufacturer usually sets the torque split.

Locally manufactured vehicles equipped with all wheel drive only (no Central Diff Locks) are:
Rav 4 2nd Gen, CRV 1st and 2nd Gen,

COMING SOON! PART TIME 4WD AND HYBRID ALL-WHELL DRIVE/PART TIME 4WD

i hope this helps in you guys apprecieating your vehicles capabilities more. :D

**Ungas** · May 22nd, 2003 09:54 AM

Cool infos! :D

**roydok** · May 22nd, 2003 07:22 PM

Nice one there. :D

**marwen** · May 22nd, 2003 08:18 PM

galing... bilib na talaga ako sa mga 4x4 nyo.... punta na kayo sa cebu.. para makasama ako kahit passenger lang...

**kiper** · May 23rd, 2003 12:44 AM

so meron ang escape ng central differential lock and viscous coupling..okay..

**OTEP** · May 23rd, 2003 01:04 AM

kiper,

The RBC viscous coupling is the center differential but it is not of the fully locking type. Mahirap kasi i-classify ang sa Escape because it breaks new grounds.

**Karding** · May 23rd, 2003 04:40 AM

ayun naman pala....great info 8)

**mazdamazda** · July 13th, 2005 08:07 PM

Originally Posted by OTEP

kiper,

The RBC viscous coupling is the center differential but it is not of the fully locking type. Mahirap kasi i-classify ang sa Escape because it breaks new grounds.

You can classify the Escape & CRV's as Automatic Asymmetric AWD.

While the Rav4 & X-Trail would be classified as Full-time Symmetric AWD.

Here's another good write-up about them:

AWD System one (true all wheel drive - or full time symmetric AWD) has a conventional differential inside the transfer case - each of the wheels gets about 25% of the torque as long as traction is equal. However, the center diff cannot be mechanically locked.

To prevent a complete loss of traction when one wheel or one axle would spin, a viscous coupling or a similar device like a Haldex coupling (see note) will try to "glue" both driveshafts together to keep enough torque flowing to the axle with traction. Works kinda OK on slippery pavement when the vehicle has already sufficient momentum and the connecting device has to kick in very infrequently. Off-road or in other situations with slow speed and high demand for torque the glue box (viscous coupling or Haldex etc.) is overstressed and fails to deliver the needed torque. High torque transfers and continous use make especially viscous couplings fail. Haldex units are much more reliable but cannot satisfy the constant high demand for torque at all wheels either.

AWD System two (automatic asymmetric AWD - and in a way actually only a sophisticated 2WD system) might not have a differential in the transfer case (Volvo, Honda, etc.) but some do (Jeep Grand Cherokee). Primary power goes only to one axle (makes spinning tires much more likely due to inefficient use of traction - as likely as in any other 2WD car). However, both drive shafts are joined by a viscous coupling or a similar device (see note) and as long as all 4 wheels turn at the same speeds the control unit remains inactive. Once the powered axle or one of the powered tires loses traction, the powered drive shaft rotates faster than the one that is just rotating along. The control unit reacts to the speed difference and kinda glues both drive shafts together. This way the previously unpowered shaft will get some of the torque and rescue the failing tires. Same story as in system one: Works kinda OK on slippery pavement when the vehicle has already sufficient momentum and the control unit has to kick in very infrequently. Fails miserably when need of high torque arises or when activated frequently. Cannot satisfy the constant high demand for torque at all wheels when off-road.